1. Field of The Invention
The present invention relates to a brake system for a vehicle and, more particularly, to an on-vehicle brake system which is capable of suppressing a pitching motion that occurs in the vehicle body at a time of the vehicle being braked.
2. Related Arts
When a braking force acts on a vehicle, the shift of a load occurs on the vehicle body in correspondence with the deceleration that occurs in the vehicle body. With the occurrence of this shift of the load, there occurs a pitching motion of a forward portion of the vehicle body being sunk or moved down and a rearward portion thereof being floated or moved up. In correspondence with this pitching motion, the upper half of a crew's body is brought to a state of its being more forwardly urged. That is, owing to the deceleration of the vehicle body, the forward urging force acts on the upper half of the crew's body and, in addition, the occurrence of the pitching motion tends to forwardly move the crew's body additionally to this forward urging force. Accordingly, at a time of the vehicle being braked, it is ordinarily required for the crew to try to remain unmoved with a considerably high magnitude of force so as for him to overcome the forwardly acting force. Further, since the pitching motion occurs most largely at around a time that is immediately before the vehicle being stopped due to the expansion and contraction of the suspensions of the vehicle, especially in a case of the vehicle being attempted to be suddenly stopped, it results that the crew becomes forwardly urged unless he exerts his considerably high magnitude of force. It is to be noted that when the brake pedal has been rapidly depressed, namely when a braking force that is greater than a prescribed value has been applied to the vehicle body, also, a large load shift occurs with the result that there occurs the pitching motion of the front side of the vehicle body being sunk and of the rear side thereof being floated.
Also, although the load is being shifted to the front side of the vehicle body until a time that is immediately before the vehicle body being stopped, especially at around a time that is immediately after the vehicle being stopped the load is shifted reversely toward the rear side of the vehicle body so as for the vehicle body to be back to its ordinary state. Therefore, at a time that is immediately after the vehicle body being stopped, as the load is shifted toward the rear side of the vehicle body, the suspensions expand or contract in a direction that is opposite to that at a time that is immediately before the vehicle being stopped, with the result that there occurs a swing-back motion of the vehicle body being swung back. In accordance with this swing-back motion of the vehicle body, a force that acts in a direction that is opposite to the direction of the force which at a time of the braking being effected is acted in the forward direction, namely, in a direction that is toward the rear side of the vehicle body, acts on the upper part of the crew's body.
In this way, by the motion of the vehicle body that is attributable to the deceleration that occurs in the vehicle body when the vehicle is braked, the force that became a burden upon the crew acted on the crew.